American journal of physiology. Regulatory, integrative and comparative physiology
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Am. J. Physiol. Regul. Integr. Comp. Physiol. · Aug 2010
Estimating changes in volume-weighted mean body temperature using thermometry with an individualized correction factor.
This study investigated whether the estimation error of volume-weighted mean body temperature (DeltaT(b)) using changes in core and skin temperature can be accounted for using personal and environmental parameters. Whole body calorimetry was used to directly measure DeltaT(b) in an Experimental group (EG) of 36 participants (24 males, 12 females) and a Validation group (VG) of 20 (9 males, 11 females) throughout 90 min of cycle ergometry at 40 degrees C, 30% relative humidity (RH) (n = 9 EG, 5 VG); 30 degrees C, 30% RH (n = 9 EG, 5 VG); 30 degrees C, 60% RH (n = 9 EG, 5 VG); and 24 degrees C, 30% RH (n = 9 EG, 5 VG). The core of the two-compartment thermometry model was represented by rectal temperature and the shell by a 12-point mean skin temperature (DeltaT(sk)). ⋯ The subsequent regression models were used to predict the thermometric estimation error (X(0_pred)) for each individual in the VG. The value estimated for X(0_pred) was then added to the DeltaT(b) estimated using the two-compartment thermometry models yielding an adjusted estimation (DeltaT(b)_(adj)) for the individuals in the VG. When comparing DeltaT(b)_(adj) to the DeltaT(b) derived from calorimetry in the VG, the best performing model used a core/shell weighting of 0.66/0.34 describing 74%, 84%, and 82% of the variation observed in DeltaT(b) from calorimetry after 30, 60, and 90 min, respectively.
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Am. J. Physiol. Regul. Integr. Comp. Physiol. · Jul 2010
Carotid sinus nerve stimulation, but not intermittent hypoxia, induces respiratory LTF in adult rats exposed to neonatal intermittent hypoxia.
We tested the hypothesis that exposure to neonatal intermittent hypoxia (n-IH) in rat pups alters central integrative processes following acute and intermittent peripheral chemoreceptor activation in adults. Newborn male rats were exposed to n-IH or normoxia for 10 consecutive days after birth. We then used both awake and anesthetized 3- to 4-mo-old rats to record ventilation, blood pressure, and phrenic and splanchnic nerve activities to assess responses to peripheral chemoreflex activation (acute hypoxic response) and long-term facilitation (LTF, long-term response after intermittent hypoxia). ⋯ In n-IH rats, respiratory LTF was not apparent in awake and anesthetized animals. Following intermittent electrical stimulation, however, phrenic LTF was clearly present in n-IH rats, being similar in magnitude to controls. We conclude that, in adult n-IH rats: 1) arterial blood pressure is elevated, 2) peripheral chemoreceptor responses to hypoxia and its central integration are not altered, but splanchnic nerve response is suppressed, 3) LTF is suppressed, and 4) the mechanisms involved in the generation of LTF are still present but are masked most probably as the result of an augmented inhibitory response to hypoxia in the central nervous system.
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Am. J. Physiol. Regul. Integr. Comp. Physiol. · Jul 2010
Thermoregulatory, behavioral, and metabolic responses to heatstroke in a conscious mouse model.
The typical core temperature (T(c)) profile displayed during heatstroke (HS) recovery consists of initial hypothermia followed by delayed hyperthermia. Anecdotal observations led to the conclusion that these T(c) responses represent thermoregulatory dysfunction as a result of brain damage. We hypothesized that these T(c) responses are mediated by a change in the temperature setpoint. ⋯ Cellular damage (hematoxylin and eosin staining) was undetectable in the hypothalamus or other brain regions in severe HS mice. Overall, decreases and increases in T(c) were associated with behavioral and autonomic thermoeffectors that suggest HS elicits anapyrexia and fever, respectively. Taken together, T(c) responses of mild and severe HS mice suggest a need for reinterpretation of the mechanisms of thermoregulatory control during recovery.
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Am. J. Physiol. Regul. Integr. Comp. Physiol. · Jun 2010
ReviewThe Walter B. Cannon Memorial Award Lecture, 2009. Physiology in perspective: The wisdom of the body. In search of autonomic balance: the good, the bad, and the ugly.
Walter B. Cannon's research on the sympathetic nervous system and neurochemical transmission was pioneering. Wisdom has endowed our body with a powerful autonomic neural regulation of the circulation that provides optimal perfusion of every organ in accordance to its metabolic needs. ⋯ This short review, presented as The Walter B. Cannon Memorial Award Lecture for 2009, addresses the mechanisms that disrupt sensory signaling and result in a chronic maladjustment of the autonomic neural output that in many cardiovascular diseases results in excessive increases in the risks of dying. The hopes for any reduction of those risks resides in an understanding of the molecular determinants of neuronal signaling.
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Am. J. Physiol. Regul. Integr. Comp. Physiol. · Jun 2010
Effect of aging on cardiac function during cold stress in humans.
To determine whether skin surface cooling increases left ventricular preload and contractility to a greater extent in older compared with young adults we studied 11 young (28 +/- 2 yr; means +/- SE) and 11 older (64 +/- 3 yr) adults during normothermia (35 degrees C water perfused through a tube-lined suit) and cooling (15 degrees C water perfused for 20 min) using standard and tissue Doppler echocardiography. Cooling significantly decreased skin surface temperature in young (Delta2.8 +/- 0.3 degrees C) and older (Delta3.0 +/- 0.3 degrees C) adults and increased rate-pressure product, an index of myocardial oxygen demand, in older (6,932 +/- 445 to 7,622 +/- 499 mmHg x beats/min for normothermia and cooling, respectively), but not young (7,085 +/- 438 to 7,297 +/- 438 mmHg x beats/min) adults. Increases in blood pressure (systolic and mean blood pressure) during cooling were greater (P < 0.05) in older than in young adults. ⋯ Indices of left ventricular contractility (ejection fraction, myocardial acceleration during isovolumic contraction, and peak systolic mitral annulus velocity) were unchanged during cooling in both young and older adults. Collectively, these data indicate that cooling increases left ventricular preload, without affecting left ventricular contractility in older but not young adults. Greater increases in preload and afterload during cooling in older adults contribute to greater increases in indices of myocardial oxygen demand and may help explain the increased risk of cardiovascular events in cold weather.